Aircraft: SMALL AIRCRAFT; HIGH WING; 1 ENG; FIXED GEAR
Phase of flight: Cruise
Anomaly: No Specific Anomaly Occurred All Types

I flew from home base to the vicinity of the city of San Francisco on a pleasure flight for sightseeing; and returned. Prior to departure; I did a thorough briefing through DUATS and checked the FAA TFR website and did not see any TFR relevant for my route of flight. During the flight; I contacted Approach for flight following; who handed me off to NORCAL Approach as I approached the San Francisco Bay Area. While maneuvering in the vicinity of the San Francisco waterfront and Alcatraz Island; and in contact with NORCAL Approach with a discrete transponder code; I heard the Controller announce on 120.9 'Attention all aircraft; AT&T Park TFR is now in effect. Remain clear; 3 NM'...or something to that effect. I was surprised by the announcement and checked my chart to ensure that I was outside the 3 NM radius. I appeared to be clear and the Controller said nothing more; so I continued my flight as planned. Upon returning home; I double checked the TFR website and did not see anything listed. Then; I recalled the 'blanket TFR'; NOTAM FDC 9/5151; which specifies a TFR around major sporting event in arenas with 30;000 seats or more; starting 1 hour before the event. Since my route of flight was not taking me 'over' a stadium; I didn't think to check on sporting events. Not being a sports fan or from the Bay Area; I had no clue that there was a baseball game that day. Not being familiar with AT&T Park; I did not know it had more than 30;000 seats. After returning home; I checked my GPS track (I typically fly with a handheld GPS to record the 'breadcrumb' trail of my flight for review and record). Using Google Earth; I found that my flight path did enter the 3 NM radius of AT&T Park briefly and that I exited the 3 NM radius zone at XA:04:50 local time. I then checked the San Francisco Giants website and found that their scheduled start time on that day was XB:05. Therefore; I exited the pending TFR airspace about 10 seconds prior to the TFR becoming active! I'm clean! Lessons learned: Clearly; I need to educate myself a little better on which stadiums qualify for a TFR and what the events schedules are when flying into a somewhat unfamiliar city. This isn't a concern for me typically; as most of my flying does not take in the vicinity of major sporting venues.Recommendations: I believe it is unreasonable to expect every pilot to know which stadiums in the United States qualify for a potential TFR under FDC 9/5151 and to expect every pilot to know game schedules for all major league games and other events that qualify. The FAA should help well intentioned pilots; like myself; who are trying their best to comply with all the regulations and restriction by at least highlighting these stadiums with a 3 NM circle on the TFR map as 'possible TFR' to help remind us to go check those schedules. Better yet; the FAA should connect with the major league schedules and simply publish those TFR's on their website explicitly; for each event. Thank you! After completing a thorough preflight and NOTAM review; a pilot entered the San Francisco Bay Area from the Central Valley for a tour with NCT flight following. He was surprised to hear ATC announce an AT&T TFR was in effect just as he departed the three NM protected area. He was not a sports fan and no had idea about the TFR because it was not in any briefing.